1. Field of the Invention
The present invention relates to a method and apparatus for locating a site and surgically positioning a dental implant. More specifically, it relates to a method and apparatus for placing an endosseous dental implant into the most optimal bone structure of a patient's upper or lower jawbone utilizing a surgical guide template that is fabricated with the use of computerized tomography and stereolithography.
2. The Prior Art
In the field of dentistry, tooth implants are increasingly being utilized. In the articles "Predictable Mandibular Nerve Location--A Clinical Zone of Safety" by Misch and Crawford, appearing in Dentistry Today, December, 1990, p. 32, and "Presurgical Prosthetics and Surgical Templates" by Zinner, Small and Panno, appearing in Dental Clinics of North America (Vol. 33, No. 4, October, 1989); and the U.S. Pat. No. 5,015,183 to Fenick describe the present state of the art regarding the placement of oral implants with a surgical template and the inherent restrictions and limitations thereof. A problem in the art and science of placing dental implants is finding and locating sufficient bone structure in height, length and width in which to fix the implant so as to obtain the most optimum long term success. In general, the longest length implant that can be placed into the greatest dimensions of bone will give the best long term prognosis.
An inherent problem exists with placing an implant into the human lower jaw. The alveolar nerve (Cranial Nerve V, Division III) passes through a canal entering the posterior areas of a human jaw and coursing through it. As a result, a surgeon is limited by the depth to which he can place an implant and presently will stay safely above the nerve, as discussed in detail in the article "Predictable Mandibular Nerve Location--A Clinical Zone of Safety." This zone of safety restricts the surgeon to only utilizing approximately one-third to one-half of the full height of available bone depending on individual anatomical variation. If an implant impinged upon the nerve, the patient could lose feeling in their lower lip and chin on the affected side. Since the location of the nerve is difficult to pinpoint during the surgical procedure with present technology, the longer more desirable types of endosseous implants generally are not used in the area of the posterior lower jaw.
If an implant could be placed in the lower posterior jaw and engage the lower portion (inferior border) this would result in improved long term prognosis. The resulting implant could be twice the length achieved by present technology.
Presently, to place an implant into the inferior border of the posterior mandible (lower jaw) it is necessary to perform a nerve transposition procedure. This involves the dissection of the nerve from its canal, followed by placing the implants. Then the nerve is repositioned around the implants. The morbidity associated with this procedure is significant. (Howard Davis, D.D.S., 1992 August, American Association of Periodontics, Chicago, Illinois--Clinical Meeting.)
Alternatively, the surgeon could use the information on a standard C.T. scan and approximate the angle of the site for the implant. However, this method presents a risk of damage to the inferior alveolar nerve which can result in altered or no sensation to the lip and chin on the affected side. The worse case scenario is an irreversible loss of feeling to the lower lip, chin and gum tissue on that side. There is a large margin for error with this method due to a lack of precision in achieving the correct angle to direct the bur during the surgical procedure of placing the implant.
Also known from the prior art are stereolithographic models (SLA Models) constructed from digital image data (computerized tomography) which allows the surgeon to view the external and internal anatomy prior to surgery, as described in the article entitled "Stereolithographic Models for Surgical Planning: Preliminary Report" by Stoker, Mankovich and Valentino, J. of Oral and Maxillofacial Surgery, May 1992, p,. 466-471. However, stereolithographic models have not been used to place dental endosseous dental implants into the most optimal jawbone location and have not been used to specifically avoid contacting the inferior alveolar nerve and more specifically to actually bypass this structure thereby engaging the lowermost portion of the jaw.
This SLA Model also gives the operating surgeon the precise information (optimal height, length and depth of bone) that is needed to fabricate a specially designed surgical template to be used in any area of the upper or lower jaw.